Al—Mn-based 3000 series alloys are relatively excellent in strength, formability, and laser weldability, so are used as materials when producing containers for lithium ion batteries and other secondary batteries. They are formed into the desired shapes, then are laser welded to seal them tight for use as containers for secondary batteries. Along with the 3000 series alloys, aluminum alloy sheets for secondary battery container use which are based on existing 3000 series alloys but are further increased in strength and formability have been developed.
For example, PLT 1 describes aluminum alloy sheet for a box shaped battery case characterized by having as the composition of the aluminum alloy sheet the composition which is prescribed in JIS A3003, having an earring ratio of 8% or less, having an average particle size of recrystallized crystal grains of 50 μm or less, and having an electrical conductivity of 45 IACS % or less.
On the other hand, as a battery case, an aluminum alloy sheet for a battery case which is excellent in swelling resistance at the time of a high temperature, internal pressure load has been developed. PLT 2 describes an aluminum alloy sheet for a battery case which is excellent in swelling resistance at the time of a high temperature, internal pressure load characterized by containing Mn: 0.8 to 2.0% (wt %, same below), being restricted in impurity elements to Si: 0.04 to 0.2% and Fe: 0.04 to 0.6%, having a balance of Al and unavoidable impurities, having an amount of Mn in solid solution of 0.25% or more, having a proof strength value of 150 to 220N/mm2 in range, and having an average area of crystal particle size at a cross-section parallel to the rolling direction of 500 to 8000 μm2 in range.
However, in an aluminum alloy sheet based on a 3000 series alloy which has been improved in composition, sometimes an abnormal bead is formed. It is known that there is a problem in laser weldability. Therefore, an aluminum alloy sheet improved in laser weldability for secondary battery container use which is based on the 1000 series is also being developed. PLT 3 describes an aluminum alloy sheet which is excellent in laser weldability which is free of uneven bead when laser welding an A1000-based aluminum material. According to this, in the aluminum alloy sheet, it is sufficient to include Si: 0.02 to 0.10 mass %, restrict the Fe content to 0.30 mass % or less, include a balance of Al and unavoidable impurities, and restrict the number of intermetallic compound particles with a circle equivalent diameter of 1.5 to 6.5 μm to 1000 to 2400/mm2.